The present disclosure relates to sound insulation materials which are to be used in places requiring sound insulation, e.g., buildings, vehicles, and aircraft, and enclose granular elastic materials of rubber or thermoplastic elastomers, and methods for preparing such sound insulation materials.
As a sound insulation material of this type, Japanese Patent Publication No. H08-185188 proposes, for example, a sound insulation material in which a granular elastic material of, for example, pulverized rubber, previously formed granular rubber, or a rubber-like elastic resin is covered with a cover layer of a sheet made of nonwoven fabric or a resin, a sound insulation material in which a latticed partition plate or a plurality of partition boxes filled with a granular elastic material is interposed between cover layers, and a sound insulation material in which the cover layer is provided integrally with a projection for separation. Japanese Patent Publication No. 2003-150169 proposes, for example, a sound insulation material prepared by filling a bag constituted by, for example, woven fabric, nonwoven fabric, or a resin film with pulverized foam particles and sealing the bag and a sound insulation material prepared by connecting, with pins or by sewing, both sides of a bag enclosing foam particles. Japanese Patent Publication No. S57-183953 proposes a packaging bag housing powder in which a center portion of the bag is sealed with heat in order to prevent collapse when bags with a uniform thickness are stacked.
A sound insulation material prepared by filling a bag with a granular elastic material has a high sound deadening property. However, in application of such a sound insulation material in a place where vibration occurs, e.g., vehicles or aircraft, vibration causes uneven distribution of a granular elastic material 2 filling a bag 1 as illustrated in FIG. 1, resulting in degradation of the sound deadening property and occurrence of a bulge of a portion in which the material 2 is locally present. To stabilize the sound deadening property and uniformize the thickness, it is necessary to prevent uneven distribution of the granular elastic material.
The above-described structures in which the inside of the bag is partitioned by the latticed partition plate or partition boxes, bags are connected together with pins or by sewing, or the center portion of the bag is sealed with heat, can inhibit movement of the granular elastic material to prevent uneven distribution of the granular elastic material and, thereby, uniformize the thickness. However, preparation of a sound insulation material by the process of filling a latticed partition plate or partition boxes with a granular elastic material, providing a cover, and then welding the rim of the cover with heat or the process of partially welding the rim of a cover with heat to form a bag, filing the bag with a granular elastic material through an unwelded portion, and then inserting pins into, or sewing, the bag, causes an increase in the number of parts, leading to a complicated structure and also an increase in the number of processes. As a result, the cost increases. In addition, in the case of connecting bags with pins, water might enter from portions at which the pins are inserted. In this aspect, in the packaging bag whose center portion is sealed with heat, heat sealing on the center portion is performed simultaneously with heat sealing on the rim of the bag. Thus, the structure and processes are simplified, thereby reducing the cost. However, in filling a bag with a granular elastic material, a center portion of the bag sealed with heat tends to be an obstacle to the filling.